The present disclosure relates generally to an engine control system and method, and particularly relates to an engine control system and method that prevents or limits automatic increasing of engine speed during a downshift of a manual transmission.
It is known to match engine speed to transmission input shaft speed upon detection of a downshift in a manual transmission. An output shaft of the engine is typically selectively connected to the main or input shaft of a transmission through a clutch. The transmission input shaft is connected to a transmission output shaft through a series of gears having gear ratios and the output shaft is connected to the vehicle's wheels, such as through a differential or similar arrangement. Gear changes of the transmission can be actuated through a shift lever.
In a known system, a vehicle's electronic control unit (ECU) is able to determine which gear the transmission is in through a sensor on the transmission input shaft and another sensor on the transmission output shaft. In particular, these sensors indicate the speeds at which the input and output shafts are rotating, and, by comparing the rotational speeds of the two shafts, the selected gear for transmission can be determined, provided the transmission is not in neutral. An engine speed sensor monitors engine speed and a neutral sensor indicates when the transmission is in neutral. Upon detection of a downshift, the ECU operates to control engine speed, such as by management of the engine's throttle or other torque application (e.g., integrated motor assist or IMA). Specifically, the ECU can attempt to match engine speed with transmission input shaft speed during and/or after a downshift. Such assistance during downshifting of a manual transmission is able to simulate “heel-toe” driving, which has the advantage of offering more power as a vehicle exits a curve and/or reduces the likelihood of a vehicle “jumping” upon engagement of the clutch after a downshift.
During downshifting of the manual transmission, it is possible to select a gear of the transmission that increases the transmission input shaft speed to a speed over which the engine is rated to operate. In this event, when the clutch reconnects the engine output shaft and the transmission input shaft, engine damage is possible depending on the length of time that the engine is overreved and/or the amount that the engine is overreved. When the engine speed is automatically increased during downshifting of the manual transmission as described above, damage to the engine can occur because its speed might be increased above a maximum speed at which the engine is rated to operate. In addition, there is less time after the clutch engages until the engine reaches a speed at which it might be compromised.